Primary hydrogen addition

On catalysts with large values of x> he chain termination probability reflects the kinetics of the primary hydrogen addition termination step, because olefin termination steps are completely reversed by extensive readsorption within a catalyst pellet. In this case, bed residence time does not affect the product distribution because olefins seldom reach interpellet voids before converting to paraffins. 

Despite the considerable driving force for the H-abstraction reaction, there is some remarkable selectivity. Primary hydrogens (-CH3) are less likely abstracted than secondary (-CH2 ) and tertiary (-CH-) ones (Asmus et al. 1973). In addition, neighboring substituents that can stabilize the resulting radical by elec-... 

The details of hydrogen transfer from carbon are unclear. Analogy with other reactions of this type, particularly those of TEMPO, would suggest a cyclic transition state, characterised by primary hydrogen effects of 2, under basic conditions and a general base-catalysed process under acidic conditions, characterised by isotope effects around 5. However, the cyclic mechanism was also proposed for the standard oxidation conditions of aqueous acetic acid, originally on the basis of a rate decrease in aqueous acetic acid as sodium acetate was added, despite such an addition possibly deprotonating the... 

Since 1973 [3] and 1975 in Dresden 2 [4], on line measurements of redox potential have been performed in the BWRs (Boiling Water Reactors) primary coolant in order to verify the IGSCC (Intergranular Stress Corrosion Craking) susceptibility of austenitic stainless steel components. Such measurements turned out to be fundamental for estimating the effect of hydrogen addition as a remedy for IGSCC [5-6]. 

Tidwell and coworkers have examined the addition of water to 1 -cyano-1 -ethoxyethene in aqueous sulphuric acid at 25 °C. The primary hydrogen-deuterium kinetic isotope effect found when the reaction is done in deuterated solvent increases from 3.77 to 5.44 as the percent sulphuric acid in the solvent increases from 6.6 M to 10.8 M. These isotope effects demonstrate that the slow step of the reaction is protonation of the vinyl substrate to form the a-cyanocarbocation and that the product is formed in subsequent, fast steps of the Ad-E2 mechanism (equation 83). 

Obviously, the nature of the reaction under these conditions will differ from the reaction in the presence of a carrier insofar as there is a direct reaction between the hydrogen and the coal. In addition, vapor-phase (or secondary) hydrogenation may also follow the primary hydrogenation in which volatile products from the decomposition of the coal or from the reaction of the coal with hydrogen then react with more hydrogen to modify the slate of primary reaction products. 

Law, R. J., Indig, M. E., Lin, C. C., Cowan, R. L. Suppression of radiolytic oxygen produced in a BWR by feedwater hydrogen addition. Proc. 3. BNES Conf Water Chemistry in Nuclear Reactor Systems, Bournemouth, UK, 1983, Vol. 2, p. 23-30 Lin, C. C. Chemical behaviour and distribution of volatile radionuclides in a BWR system with forward-pumped heater drains. Proc. 3. BNES Conf. Water Chemistry in Nuclear Reactor Systems, Bournemouth, UK, 1983, Vol. 1, p. 103—110 Lin, C. C. Chemical behaviour and steam transport of nitrogen-13 in BWR primary systems. 

The isotopic composition of fission product iodine present in the BWR reactor water in the case of failed fuel rods in the reactor core is quite similar to that in the PWR primary coolant. Since the iodine purification factor of the reactor water cleanup system is on the order of 100, i. e. virtually identical to that of the PWR primary coolant purification system, this similarity in isotopic composition demonstrates that the release mechanisms of iodine isotopes from the failed fuel rods to the water phase are virtually identical under both PWR and BWR operating conditions. On the other hand, the resulting chemical state of fission product iodine in the BWR reactor water is quite different from that in the PWR primary coolant. The BWR reactor water usually does not contain chemical additives (with the possible exception of a hydrogen addition, see below) as a result of water radioly-... 

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